1. Field of the Invention
This invention relates to a process and apparatus for production of fuels by photoelectrolysis of water and photooxidation of water soluble biomass product. More particularly, this invention relates to production of hydrogen by photoelectrolysis of water as the cathodic reaction of an optically illuminated photochemical diode in contact with an electrolyte which comprises a biomass product which may be monosaccharides, polysaccharides, lignins, their partially oxidized products, and mixtures thereof which are oxidized as the anodic reaction of the photochemical diode producing liquid fuels and useful chemicals. Molecular oxygen evolution is avoided in the process of this invention. The process of this invention produces high purity hydrogen photoelectrolytically at potentials substantially less than required for normal water electrolysis involving oxygen evolution. The utilization of biomass product provides a cost effective material to increase fuels production by photoelectrolysis of water.
2. Description of the Prior Art
Photoelectrolysis of water by solar radiation has been proposed by several techniques as exemplified by U.S. Pat. Nos. 4,090,933 and 4,011,149 and references cited therein.
Photochemical diodes, in the form of Schottky-type diodes or p-n type diodes are taught by U.S. Pat. No. 4,094,751 to be useful to convert water into hydrogen plus oxygen (or hydrogen peroxide) and to convert hydrogen sulfide into hydrogen plus sulfur.
The electrolytic oxidation of dextrose in the manufacture of calcium gluconate is known as described in the article "Manufacture of Calcium Gluconate by Electrolytic Oxidation of Dextrose" by H. S. Isbell, Harriet L. Frush and F. J. Bates, Industrial and Engineering Chemistry, Vol. XXIV, No. 4, April 1932, pps. 375-378, wherein it is taught that CaBr.sub.2 is necessary as a catalyst. U.S. Pat. No. 1,976,731 teaches the electrolytic oxidation of an aldose sugar in the presence of a halogen salt catalyst having atomic weight greater than chlorine. The article "Electrolytic Preparation of Calcium Gluconate and Other Salts of Aldonic Acids" by Colin G. Fink and Donald B. Summers, Transactions of the Electrochemical Society, 74, 625 (1938), teaches that alkali ferricyanide may be used as a substitute for the alkali bromide as a catalyst in the electrolytic preparation of calcium gluconate. The commercial processes for oxidation of sugars to acids are indirect oxidations, that is, the electrochemical reaction is reduction of bromine followed by a subsequent chemical oxidation reaction.
U.S. Pat. No. 4,089,761 teaches a sewage treatment process wherein oxygen for supply to aerobic microorganisms is produced at the anode of an electrolytic cell maintained in the biodigestion compartment of the sewage treatment cell with the cathode being isolated so as to vent hydrogen out of the cell.
The applicants are not aware of prior art wherein photochemical diodes are contacted by an aqueous electrolyte comprising biomass product which, upon exposure of the photochemical diodes to optical energy, produces molecular hydrogen and oxidized biomass product, both of which readily provide useful fuels. The production of molecular oxygen is avoided in the process of the present invention and the photochemical diodes having band gaps of less than about 2 eV are stabilized against corrosion.